AISI 4140 steel is a low alloy steel containing chromium, molybdenum, and manganese. It is widely used across numerous industries and is an excellent material choice due to its toughness, high fatigue strength, and abrasion and impact resistance.

CHEMICAL COMPOSITION

HEAT TREATMENT OPTION

• +A: Annealed (full/soft/spheroidizing)
• +N: Normalized
• +NT: Normalized and tempered
• +QT: Quenched and tempered (water/oil)

FABRICATION AND HEAT TREATMENT

Machinability
AISI 4140 alloy steel has good machinability in the annealed condition.

Forming
AISI 4140 alloy steel has high ductility. It can be formed using conventional techniques in the annealed condition. It requires more pressure or force for forming because it is tougher than plain carbon steels.

Welding
AISI 4140 alloy steel can be welded using all conventional techniques. However, the mechanical properties of this steel will be affected if it is welded in the heat-treated condition, and post-weld heat treatment should be performed.

Heat Treatment
AISI 4140 alloy steel is heated at 845°C (1550°F) followed by quenching in oil. Before hardening, it can be normalized by heating it at 913°C (1675°F) for a long period of time, followed by air cooling.

Forging
AISI 4140 alloy steel is forged at 926 to 1205°C (1700 to 2200°F)

Hot Working
AISI 4140 alloy steel can be hot worked at 816 to 1038°C (1500 to 1900°F)

Cold Working
AISI 4140 alloy steel can be cold worked using conventional methods in the annealed condition.

Annealing
AISI 4140 alloy steel is annealed at 872°C (1600°F) followed by slowly cooling in the furnace.

Tempering
AISI 4140 alloy steel can be tempered at 205 to 649°C (400 to 1200°F) depending upon the desired hardness level. The hardness of the steel can be increased if it has a lower tempering temperature. For example, a tensile strength of 225 ksi can be achieved by tempering at 316°C (600°F), and tensile strength of 130 ksi can be achieved by tempering at 538°C (1000°F).

Hardening
AISI 4140 alloy steel can be hardened by cold working, or heating and quenching.